Detergents comprising anionic detersive surfactants for cleaning fabrics have been known for many years. Historically, cleaning laundry was defined primarily as a process that involved removal of stains. Consistent with this historical approach to cleaning, laundry detergent designers focused on formulating detergents with surfactants with longer carbon chains to ensure maximum surface activity of the surfactants to achieve the most effective soil removal.
Such long-chain surfactants can generate copious suds during wash cycles of the fabric laundering process. Therefore, consumers view high suds volume as the primary and most desirable signal of cleaning. For hand-washing consumers, who are still the dominating majority in most developing countries, high suds volume are especially desirable, since the consumers can directly feel and touch suds generated during the hand-washing process and intuitively correlate high suds volume with sufficient fabric cleaning.
Paradoxically, high volume of suds during the wash cycle will typically translate to more suds in the subsequent rinse cycle. When consumers observe suds during the rinse cycle, they immediately infer from it that there may still be surfactant residue on the fabrics. Surfactant residue remaining on the fabrics may cause irritation to the skin, and it may also render the fabrics “sticky” after drying, thereby likely to attract more dirt upon wearing. Consequently, the consumers will feel the need to rinse the fabric a few more times, until suds are completely or substantially disappeared from the rinse solution, signaling that the fabrics are now “clean” and free of surfactant residue. However, oftentimes one or two rinses are sufficient to remove most or all of surfactant residue from the fabrics, despite a significant amount of suds remaining in the rinse solution. In other words, the additional rinses are unnecessary and excessive. Such excessive rinsing requires additional time, labor, energy and water. For regions where resources are scarce, especially those regions suffering from water shortage, excessive rinsing is particularly undesirable.
Therefore, a sudsing profile of a detergent composition during both wash and rinse cycles of the fabric laundering process is important for the overall consumer laundering experience, particularly for hand-washing consumers.
There is a need to provide consumers with an improved laundry cleaning (i.e., laundering) experience, especially those consumers who are accustomed to manually washing their laundry, either entirely (i.e., full manual/hand laundering) or in conjunction with machine washing (i.e., semi-automatic laundering). Specifically, this improved laundering experience is enabled by a desired sudsing profile defined by at least four (4) key points of consumer observation (hereinafter “touch points”), which jointly connote to the consumer that the laundry is sufficiently cleaned and rinsed. A failure at any one of these touch points may result in the consumer having a less than an ideal laundering experience.
These four (4) touch points, which are hereby labeled as “Flash Suds,” “Suds Mileage,” “Initial Rinse Suds,” “End Rinse Suds,” are explained hereinafter with reference to FIG. 1, which illustrates a typical laundering process with a wash cycle followed by a rinse cycle. Prior to the wash cycle, i.e., during a pre-wash step, a consumer will dissolve a laundry detergent product in a specific amount of water to form aqueous wash liquor, and the laundry to be treated will be brought into contact with the wash liquor.
The wash cycle starts with mechanical agitation of the laundry with the wash liquor, either in a washing machine or directly by the hands of the consumer, which leads to an initial bloom of suds that is characterized by a significantly high volume of suds (measured by height) generated at a relatively high speed (within the first 2-3 minutes of the wash cycle) during a first stage of the wash cycle, i.e., the “W-1” stage shown in FIG. 1. This initial bloom of suds, or the so-called “Flash Suds,” constitutes the first touch point, which signals that the surfactant in the laundry detergent is working effectively to clean the laundry. The second touch point calls for sustainment or maintenance of the wash suds volume or height at a relatively level, i.e., the so-called “Suds Mileage,” throughout a second, subsequent stage of the wash cycle (the “W-2” stage shown in FIG. 1).
These two initial touch points indicate to the consumer that the laundry detergent is efficacious in cleaning the laundry and remains so throughout the entire wash cycle. If there are no flash suds or if the flash suds volume is not high enough at the W-1 stage, then the consumer may interpret that the laundry detergent product as not being efficacious. If the suds mileage is not maintained throughout a significant portion of the W-2 stage of the wash cycle, the consumer may interpret that the laundry detergent product is losing cleaning efficacy or that there is not enough surfactant in the detergent to effectively clean the entire laundry bundle.
After the wash cycle and before the rinse cycle, i.e., during an in-between step, the sufficiently washed laundry is separated from the wash liquor. The wash liquor is drained or otherwise disposed. The laundry is wrung or spun to remove any excess wash liquor, followed by contacting the laundry with clean water or a rinse solution. The suds volume (measured by height) during this in-between step is inconsequential to the consumer, so it is not measured, and the dotted line only indicates the approximate suds volume (measure by height) during this step for illustration purposes.
During the rinse cycle, mechanical agitation (either by machine or by hand) is also applied to the laundry in the rinse solution, in attempt to rinse any carry-over or residue surfactant and soil off the laundry. At a first stage of the rinse cycle, i.e., the “R-1” stage in FIG. 1, some initial suds may be observed in the rinse solution, which is referred to as the “Initial Rinse Suds.” A portion of such initial rinse suds as shown in FIG. 1 is carried over by the laundry from the wash cycle, i.e., residue suds attached to the laundry. The remaining portion of the initial rinse suds is generated by mechanical agitation of the rinse solution, due to the presence of carry-over or residue surfactant therein. Such initial rinse suds constitute the third touch point, which is preferably of a moderate volume (measured by height). The consumer expects to see some initial rinse suds, given the carryover of surfactant from the washed laundry. Complete absence of initial rinse suds may cause the consumer to doubt the efficacy of previous wash cycle.
The fourth touch point calls for fast and significant withering of suds (indicated by the dotted arrowhead) at a second, subsequent stage of the rinse cycle (the “R-2” stage of FIG. 1) that leads to a zero or near-zero “End Rinse Suds” volume (measured by height). Despite continued agitation, the rinse suds volume (measured by height) decreases significantly and quickly during this stage to a zero or near zero level. Note that both magnitude and speed of such suds decrease at the R-2 stage are important, because jointly they signal effective rinsing of the laundry. At the end of the R-2 stage, the rinse suds are eliminated or nearly eliminated, which connotes to the consumer that most or all of the residue surfactant has been rinsed off the laundry and he/she can move on to the post-rinse step, e.g., drying and/or ironing the laundry. Accordingly, the consumer can confidently stop rinsing and end the laundering process, which will help not only to save water but also to save the consumer's time.
During the R-2 stage, if the rinse suds decrease is not significant or fast enough to lead to zero or near-zero End Rinse Suds volume (measured by height), it connotes to the consumer that there is still residue surfactant in the washed laundry or the rinse solution. Consequently, the consumer feels that the rinse is not completed yet and may needlessly spend additional time rinsing and/or using additional rinse water until all of the suds are eliminated or nearly eliminated. Therefore, it is important that the fourth touch point is present to connote that the detergent product can be easily rinsed away from the washed laundry, i.e., it is an easy-rinse formulation, which can provide a key point of differentiation for laundry detergent products.
A laundry detergent product that provides an optimized sudsing profile at all four touch points discussed hereinabove connotes high cleaning efficacy as well as the easy rinse benefits of the laundry detergent product. It may also help the consumer to save water and/or may reduce the time the user takes in rinsing the laundry. Conventional laundry detergents may provide a laundering experience at one or more of these touch points, but never has a product provided consumers with an optimized sudsing profile at all four of these touch points (while also providing cleaning efficacy). Accordingly, there is a need for such a laundry detergent product.